1. Field of the Invention
This invention relates to valve control apparatuses for engines and to diesel engine brakes.
2. Description of Related Art
Internal combustion engines conventionally have at least one exhaust valve and at least one intake valve per cylinder. The opening and closing of the valves is governed by a camshaft which rotates at one half engine speed. In most engines the timing of valve opening and closing cannot be regulated and occurs at fixed points on the engine cycle.
Devices have however been developed to alter valve timing, for example as disclosed in U.S. Pat. No. 4,870,930 to Yagi. Here an electromagnetic solenoid operates on a valve stem to hold the valve open longer than normal.
In U.S. Pat. No. 4,662,332 to Bergmann, an engine brake operates by holding valves open during braking with hydraulic actuators. The device requires pistons large enough to hold the valves open with available oil pressure used as an hydraulic fluid. The device also uses an exhaust restrictor to increase the braking effect.
In U.S. Pat. No. 4,466,390 to Babitzka, a fluid column is interposed between the cam and the valve. Valve timing can be regulated by trapping fluid in the column or allowing it to drain. The complicated arrangement is not well adapted for retrofitting existing engines.
In some engine applications the force available from an electromagnetic device, as disclosed in the Yagi patent, may not be sufficient to hold the valve open. Also Yagi discloses holding the valve open only a relatively brief period on the exhaust stroke and does not conceive of a device where the holding open of the exhaust valve can be utilized for engine braking purposes.
It may be desirable to retrofit engines with valve control apparatuses, for example when adapted for use as a diesel engine brake. Devices such as in the patent to Babitzka are not suitable, as discussed.